ci: enable GitHub Actions workflows to support fork PRs

[chambridge]

Description

Refactor CI workflows to handle fork PRs which have limited permissions and cannot post comments directly.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test coverage improvement

Related Issues

Fixes "Resource not accessible by integration" errors for external contributor PRs from forks.

Changes Made

• ci.yml: Save coverage data as artifact instead of posting comment directly (which fails on forks due to permissions)
• coverage-comment.yml: New workflow using workflow_run trigger to post coverage comments with write permissions in upstream context. Includes security validation of PR number to prevent cross-PR comment injection.
• pr-review-auto-fix.yml: Add allowed_non_write_users: '*' to enable Claude Code Review on fork PRs (claude-code-action#579)

Testing

• actionlint: All 3 workflow files pass validation (ci.yml, coverage-comment.yml, pr-review-auto-fix.yml)

• Security review: Validated PR number injection mitigation - uses trusted PR number from GitHub API, not artifact

• No runtime tests: Workflow changes can only be fully tested when triggered by actual fork PRs in the upstream repo

• Unit tests pass (pytest)

• Integration tests pass

• Manual testing performed

• No new warnings or errors

Checklist

• My code follows the project's code style
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Screenshots (if applicable)

Additional Notes

[github-actions]

🎉 This PR is included in version 2.22.1 🎉

The release is available on GitHub release

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